This application claims priority to an application entitled Device and Method for Controlling Transmission Power of Mobile Station in Multi-Carrier CDMA Mobile Communication System filed in the Korean Industrial Property Office on Dec. 3, 1998 and assigned Ser. No. 98-52758, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a power control device and method in a CDMA mobile communication system, and in particular, to a reverse link power control device and method in a multi-carrier CDMA mobile communication system.
2. Description of the Related Art
A CDMA (Code Division Multiple Access) mobile communication system performs power control in order to enable communication between a base station and a mobile station at proper power. Such power control can be divided into forward power control and reverse power control. With regard to forward power control, the base station controls its transmission power to transmit information to the mobile station at proper power. With regard to reverse power control, the base station measures receiving power of a signal transmitted from the mobile stations in order to control the transmission power of the mobile station.
More specifically, with regard to reverse power control, the receiving side (i.e., base station) measures receiving power of a signal transmitted from at least one transmission side (i.e., mobile station), and provides a power control bit (PCB) corresponding to the measured results to the transmission side so that the transmission side can control its transmission power.
Existing CDMA mobile communication systems employ a single carrier system as defined by IS-95A and IS-95B. Accordingly, the base station transmits the PCB for reverse power control with respect to only one carrier, and the mobile station also extracts the PCB with regard to only one carrier when performing power control. For example, when receiving power of a signal transmitted from the mobile station is higher or lower than a threshold, the base station transmits the PCB for increasing or decreasing transmission power of the mobile station, with regard to only one carrier. The mobile station then analyzes the transmitted PCB for the single carrier, and increases or decreases its transmission power to obtain a corresponding power level of the reverse link.
FIG. 1 is a diagram for explaining a power control procedure in a CDMA mobile communication system using a single carrier. Referring to FIG. 1, in an IS-95 mobile communication system, a 20 ms frame is comprised of 16 power control groups (PCGs),of 1.25 ms duration. Each 1.25 ms power control group is divided into 24 symbol durations, one or two of first 16 symbols being punctured for the PCBs. In the case where the I-channel and the Q-channel is transmitted over the traffic channel different from each other, only one of 16 symbols is punctured. In the case where the I-channel and the Q-channel are transmitted over the same traffic channel, two consecutive symbols of 16 symbols are punctured.
Further, a starting point of the PCB is determined by a 4-bit long code mask corresponding to the last 4 symbols of the 24 symbols constituting the previous PCG.
Future CDMA mobile communication systems will adopt a multi-carrier system defined by IMT-2000. Therefore, it is necessary to define a power control method for such a multi-carrier system.
It is, therefore, an object of the present invention to provide a device and method for performing reverse power control in a multi-carrier CDMA mobile communication system. Reverse power control refers to adjusting the transmission power of the transmission side or mobile station.
It is another object of the present invention to provide a device and method for controlling transmission power of a mobile station based on at least one power control bit extracted from a multi-carrier signal transmitted from a base station in a CDMA mobile communication system.
To achieve the above object, there is provided a device for controlling transmission power of a mobile station in a multi-carrier CDMA mobile communication system. The device includes a digital mixer for dividing received wide band multi-carrier signals according to, carriers and filtering the divided carrier signals. A searcher separates the divided carrier signals according to carrier signals which have sustained the same path delay. Fingers perform despreading and demodulation on the carrier signals which have experienced the same path delay, the carrier signals being provided in parallel from the digital mixer. The fingers also synchronize the demodulated signals. Parallel/serial (P/S) converters convert the demodulated signals provided in parallel from the fingers to serial signals and de-randomizers de-randomize the converted demodulated serial signals using a subscriber identification code. A combiner divides the de-randomized demodulated signals according to cells, and provides a transmission device of a mobile station with a transmission gain control signal for reverse power control according to power control bits extracted from the divided demodulated signals.